Dust events characterization from visibility, trends and Dust Adversity Index in the Canary Islands for the period 1980-2022

Dust events in the Canary Islands have been documented since the late 19th century. However, during the past few years, several severe dust episodes have occurred in the Canary Islands, resulting in significant impacts on various sectors, such as aviation, air quality, and health, among others. These recent severe events have drawn the attention of both scientists and the general population, raising questions about whether these episodes are now more frequent and more severe. This study analyzes 483 dust events recorded in the Canary Islands over the last 40 years. Data analysis reveals that the average number of dust event days per year is approximately 24 days, and these events have an average duration of 1.8 days, both of which show a statistically significant decreasing trend over the series. Seasonal examination indicates that events occurring in the first and fourth quarters of the year have twice the duration of those in the other quarters. Furthermore, on an annual basis, events in the first quarter exhibit negative trends in both average and minimum visibilities. This suggests that dust events in the Canary Islands are becoming shorter in duration but more intense in terms of visibility. In this article, the Dust Adversity Index (DAI) is introduced to objectively compare the severity of events. Finally, anomalies in geopotential have been utilized to determine the prevailing synoptic patterns during dust events. It is evident that the dominant synoptic pattern during the first and fourth quarters of the year consists of a low cut-off system located to the west of the Canary Islands and a high-pressure system to the north of the Iberian Peninsula.

Climate change and Saharan dust drive recent cladoceran and primary production changes in remote alpine lakes of Sierra Nevada, Spain

Recent anthropogenic climate change and the exponential increase over the past few decades of Saharan dust deposition, containing ecologically important inputs of phosphorus (P) and calcium (Ca), are potentially affecting remote aquatic ecosystems. In this study, we examine changes in cladoceran assemblage composition and chlorophyll-a concentrations over the past ~150 years from high-resolution, well-dated sediment cores retrieved from six remote high mountain lakes in the Sierra Nevada Mountains of Southern Spain, a region affected by Saharan dust deposition. In each lake, marked shifts in cladoceran assemblages and chlorophyll-a concentrations in recent decades indicate a regional-scale response to climate and Saharan dust deposition. Chlorophyll-a concentrations have increased since the 1970s, consistent with a response to rising air temperatures and the intensification of atmospheric deposition of Saharan P. Similar shifts in cladoceran taxa across lakes began over a century ago, but have intensified over the past ~50 years, concurrent with trends in regional air temperature, precipitation, and increased Saharan dust deposition. An abrupt increase in the relative abundance of the benthic cladoceran Alona quadrangularis at the expense of Chydorus sphaericus, and a significant increase in Daphnia pulex gr. was a common trend in these softwater lakes. Differences in the magnitude and timing of these changes are likely due to catchment and lake-specific differences. In contrast with other alpine lakes that are often affected by acid deposition, atmospheric Ca deposition appears to be a significant explanatory factor, among others, for the changes in the lake biota of Sierra Nevada that has not been previously considered. The effects observed in Sierra Nevada are likely occurring in other Mediterranean lake districts, especially in softwater, oligotrophic lakes. The predicted increases in global temperature and Saharan dust deposition in the future will further impact the ecological condition of these ecosystems.

The MERRA-2 Aerosol Reanalysis, 1980 Onward. Part II: Evaluation and Case Studies

The Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2), is NASA's latest reanalysis for the satellite era (1980 onward) using the Goddard Earth Observing System, version 5 (GEOS-5), Earth system model. MERRA-2 provides several improvements over its predecessor (MERRA-1), including aerosol assimilation for the entire period. MERRA-2 assimilates bias-corrected aerosol optical depth (AOD) from the Moderate Resolution Imaging Spectroradiometer and the Advanced Very High Resolution Radiometer instruments. Additionally, MERRA-2 assimilates (non bias corrected) AOD from the Multiangle Imaging SpectroRadiometer over bright surfaces and AOD from Aerosol Robotic Network sunphotometer stations. This paper, the second of a pair, summarizes the efforts to assess the quality of the MERRA-2 aerosol products. First, MERRA-2 aerosols are evaluated using independent observations. It is shown that the MERRA-2 absorption aerosol optical depth (AAOD) and ultraviolet aerosol index (AI) compare well with Ozone Monitoring Instrument observations. Next, aerosol vertical structure and surface fine particulate matter (PM_2.5) are evaluated using available satellite, aircraft, and ground-based observations. While MERRA-2 generally compares well to these observations, the assimilation cannot correct for all deficiencies in the model (e.g., missing emissions). Such deficiencies can explain many of the biases with observations. Finally, a focus is placed on several major aerosol events to illustrate successes and weaknesses of the AOD assimilation: the Mount Pinatubo eruption, a Saharan dust transport episode, the California Rim Fire, and an extreme pollution event over China. The article concludes with a summary that points to best practices for using the MERRA-2 aerosol reanalysis in future studies.

Linking Endotoxins, African Dust PM10 and Asthma in an Urban and Rural Environment of Puerto Rico

African Dust Events (ADE) are a seasonal phenomenon that has been suggested to exacerbate respiratory and proinflammatory diseases in Puerto Rico (PR). Increases in PM₁₀ concentration and the effects of biological endotoxins (ENX) are critical factors to consider during these storms. ENX promote proinflammatory responses in lungs of susceptible individuals through activation of the Toll-like receptors (TLR2/4) signaling pathways. The objective of the study was to evaluate the toxicological and proinflammatory responses stimulated by ADE PM₁₀ ENX reaching PR using human bronchial epithelial cells. PM₁₀ organic extracts from a rural and urban site in PR (March 2004) were obtained from ADE and non-ADE and compared. A retrospective data analysis (PM₁₀ concentration, aerosol images, and pediatric asthma claims) was performed from 2000 to 2012 with particular emphasis in 2004 to classify PM samples. Urban extracts were highly toxic, proinflammatory (IL-6/IL-8 secretion), and induced higher TLR4 expression and NF-κB activation compared to rural extracts. ENX were found to contribute to cytotoxicity and inflammatory responses provoked by urban ADE PM₁₀ exposure suggesting a synergistic potency of local and natural ENX incoming from ADE. The contribution of ADE PM₁₀ ENX is valuable in order to understand interactions and action mechanisms of airborne pollutants as asthma triggers in PR.

Dryness of ephemeral lakes and consequences for dust activity: the case of the Hamoun drainage basin, southeastern Iran

This study examines the influence of changes in the water coverage in the Hamoun dry-bed lakes on visibility, dust outbreaks, aerosol loading and land-atmospheric fluxes over the region covering the period 1985-2005. The Hamoun basin, located on the southeastern Iran and western Afghanistan borders, has been recognized as one of the major dust source regions in south Asia and is covered by shallow, marshy lakes that are fed by the Helmand and Farahrood rivers. When the water in watersheds that support the lakes is drawn down for natural or human-induced reasons, the end result is a decrease in the water coverage in the basin, or even complete dryness as occurred in 2001. Then, strong seasonal winds, mainly in summer, blow fine sand and silt off the exposed lakebed, enhancing dust activity and aerosol loading over the region. Satellite (Landsat) and meteorological observations reveal that the water levels in the Hamoun lakes exhibit considerable inter-annual variability during the period 1985-2005 strongly related to anomalies in precipitation. This is the trigger for concurrent changes in the frequency of the dusty days, aerosol loading and deterioration of visibility over the region, as satellite (TOMS, MODIS, MISR) observations reveal. On the other hand, soil moisture and latent heat, obtained via model (GLDAS_noah-10) simulations are directly linked with water levels and precipitation over the region. The desiccation of the Hamoun lakes in certain years and the consequent increase in frequency and intensity of dust storms are serious concerns for the regional climate, ecosystems and human health.

African Dust Storms Reaching Puerto Rican Coast Stimulate the Secretion of IL-6 and IL-8 and Cause Cytotoxicity to Human Bronchial Epithelial Cells (BEAS-2B)

African dust storm events (ADE) travel across the Atlantic Ocean (ADEAO) and reach the Puerto Rican coast (ADEPRC), potentially impacting air quality and human health. To what extent seasonal variations in atmospheric particulate matter (PM) size fractions, composition and sources trigger respiratory-adverse effects to Puerto Ricans is still unclear. In the present study, we investigated the pro-inflammatory and cytotoxic effects of PM samples harvested during ADEAO (PM10), ADEPRC (PM2.5 and PM10) and Non-ADE (Preand Post-ADEAO and Non-ADEPRC), using BEAS-2B cells. Endotoxins (ENX) in PM2.5 and PM10 extracts and traces of metals (TMET) in PM2.5 extracts were also examined. IL-6 and IL-8 secretion and cytotoxicity were used as endpoints. ADEAO and ADEPRC extracts were found to be more cytotoxic than Non-ADE and ADEAO were more toxic than ADEPRC extracts. PM10 extracts from ADEAO and Post-ADEAO caused significant secretion of IL-8. IL-6 and IL-8 secretion was higher following treatment with PM10 and PM2.5 ADEPRC than with Non-ADEPRC extracts. ENX levels were found to be higher in PM10 ADEAO than in the rest of the samples tested. TMET levels were higher in PM2.5 ADEPRC than in Non-ADEPRC extracts. Deferoxamine significantly reduced cytotoxicity and IL-6 and IL-8 secretion whereas Polymyxin B did not. TMET in PM2.5 fractions is a major determinant in ADEPRC-induced toxicity and work in conjunction with ENX to cause toxicity to lung cells in vitro. ENX and TMET may be responsible, in part, for triggering PM-respiratory adverse responses in susceptible and predisposed individuals.

Are vegetation-related roughness changes the cause of the recent decrease in dust emission from the Sahel?

[1] Since the 1980s, a dramatic downward trend in North African dustiness and transport to the tropical Atlantic Ocean has been observed by different data sets and methods. The precise causes of this trend have previously been difficult to understand, partly due to the sparse observational record. Here we show that a decrease in surface wind speeds associated with increased roughness due to more vegetation in the Sahel is the most likely cause of the observed drop in dust emission. Associated changes in turbulence and evapotranspiration, and changes in large-scale circulation, are secondary contributors. Past work has tried to explain negative correlations between North African dust and precipitation through impacts on emission thresholds due to changes in soil moisture and vegetation cover. The use of novel diagnostic tools applied here to long-term surface observations suggests that this is not the dominating effect. Our results are consistent with a recently observed global decrease in surface wind speed, known as "stilling", and demonstrate the importance of representing vegetation-related roughness changes in models. They also offer a new mechanism of how land-use change and agriculture can impact the Sahelian climate. Citation: Cowie, S. M., P. Knippertz, and J. H. Marsham (2013), Are vegetation-related roughness changes the cause of the recent decrease in dust emission from the Sahel?, Geophys. Res. Lett., 40, 1868-1872, doi:10.1002/grl.50273.

Atmospheric particulate matter levels, chemical composition and optical absorbing properties in Camagüey, Cuba

Atmospheric aerosol particles were collected at Camagüey, Cuba, during the period from February 2008 to April 2009 in order to know the particulate matter levels (PM) together with a general chemical and absorption characterization. The aerosols collection was carried out with a low volume particulate impactor twice a week. Gravimetric analysis of the particulate matter fractions PM10 and PM1 was carried out. An analysis of the eight major inorganic species (Na (+), K(+), Ca(2+), Mg(2+), NH4 (+), Cl(-), NO3(-) and SO4 (2-)) using ionic chromatography was conducted. The results were analyzed in two periods, the high aerosol concentration period (May to August) and the period with low aerosol concentration (the other months). During the high concentration period the average PM10 and PM1 levels were 35.11 μg m (-3) (std = 15.45 μg m(-3)) and 16.86 μg m(-3) (std = 6.14 μg m (-3)). During the low concentration period the average PM10 and PM1 levels were 23.13 μg m (-3) (std = 5.00 μg m(-3)) and 13.00 μg m(-3) (std = 4.02 μg m (-3)). For both periods, Cl(-), Na(+) and NO3 (-) are the predominant species in the coarse fraction (PM1-10), and SO 4(2-)and NH4(+) are the predominant species in the fine fraction (PM1). The spectral aerosol absorption coefficient, σ a, was measured for the wavelength range 400-700 nm with 10 nm steps. The σ a values were obtained with a filter transmission method for the fine fraction and were evaluated for 54 days covering a wide range of atmospheric conditions including a Saharan dust intrusion. σ a ranges from 8.5 M m(-1) to 34.5 M m(-1) at a wavelength of 550 nm, with a mean value of 18.7 M m (-1). The absorption Ångström parameter, αa, calculated for the pair of wavelengths (450/700 nm) presents a mean value of 0.33 (std = 0.19), which is a very low value comparing with those that can be found in the bibliography. Although the sampling period is short, these data represent the first evaluation of PM values with their chemical and optical absorption characterization in Cuba. In addition to the regional interest, the presented values can be directly used by those working with absorption, forcing by aerosols and radiative transfer calculations in general. Also, these data can be used as input in Global Climate Models.

Atmospheric transport and deposition of mineral dust to the ocean: implications for research needs

This paper reviews our knowledge of the measurement and modeling of mineral dust emissions to the atmosphere, its transport and deposition to the ocean, the release of iron from the dust into seawater, and the possible impact of that nutrient on marine biogeochemistry and climate. Of particular concern is our poor understanding of the mechanisms and quantities of dust deposition as well as the extent of iron solubilization from the dust once it enters the ocean. Model estimates of dust deposition in remote oceanic regions vary by more than a factor of 10. The fraction of the iron in dust that is available for use by marine phytoplankton is still highly uncertain. There is an urgent need for a long-term marine atmospheric surface measurement network, spread across all oceans. Because the southern ocean is characterized by large areas with high nitrate but low chlorophyll surface concentrations, that region is particularly sensitive to the input of dust and iron. Data from this region would be valuable, particularly at sites downwind from known dust source areas in South America, Australia, and South Africa. Coordinated field experiments involving both atmospheric and marine measurements are recommended to address the complex and interlinked processes and role of dust/Fe fertilization on marine biogeochemistry and climate.

Scattering properties of sands. 2. Results for sands from different origins

Mineral sand is a major component of aerosols in the atmosphere. It is necessary to have a laboratory database to interpret the remote sensing measurements of light scattered by such grains. For this purpose, the PROGRA2 experiment is dedicated to the retrieval of polarization and brightness phase curves, in the visible wavelength domain, of various grains that can be found in Earth's atmosphere and in space. The measurements of the scattered light by levitating clouds of grains are conducted at two wavelengths, 632.8 and 543.5nm, with PROGRA2-VIS. Large grains (at least tens of micrometers) are studied in microgravity conditions during parabolic flights; smaller (micrometer-sized) grains are lifted by an air draught in ground-based conditions. The PROGRA2-SURF instrument allows measurements on the grains deposited on a plane surface, at the same wavelengths. New data for the scattering properties are presented for sands of various origins, including fine clay. The polarimetric phase curves for levitating grains are close to each other for all the samples (except for black sands); small discrepancies are mainly due to grains' light absorption differences. The polarization curves for levitating grains differ strongly from those of deposited grains (dry or wet). In particular, these curves can be used to interpret remote sensing measurements to distinguish between grains at ground and grains transported by winds.

Dust storms: recent developments

Dust storms have a number of impacts upon the environment including radiative forcing, and biogeochemical cycling. They transport material over many thousands of kilometres. They also have a range of impacts on humans, not least on human health. In recent years the identification of source areas for dust storms has been an important area or research, with the Sahara (especially Bodélé) and western China being recognised as the strongest sources globally. Another major development has been the recognition of the degree to which dust storm activity has varied at a range of time scales, millennial, century, decadal, annual and seasonal.

Relationship between African dust carried in the Atlantic trade winds and surges in pediatric asthma attendances in the Caribbean

Asthma is epidemic in developed and developing countries including those in the Caribbean where it is widely believed that African dust, transported in high concentrations in the Trade Winds every year, is a major causative factor. The link between asthma and dust in the Caribbean is based largely on anecdotal evidence that associates sharp increases in the occurrence of asthma symptoms with hazy conditions often caused by dust. Here we report on a 2-year study of the relationship between the daily concentrations of dust measured in on-shore Trade Winds at Barbados and pediatric asthma attendance rates at Queen Elizabeth Hospital (QEH). We looked for large increases in QEH daily attendances in relation to daily dust concentrations as previously suggested by anecdotal observations. We could not find any obvious relationship although there may be more subtle linkages between dust and asthma. Our measurements show, however, that the concentration of dust in the size range under 2.5 microm diameter is sufficiently high as to challenge United States Environmental Protection Agency air quality standards for respirable particles. Thus, African dust may constitute a health threat of a different nature, producing symptoms less obvious than those of asthma.